1. Field of the Invention
This invention relates to a developing apparatus for developing an electrostatic image on an image bearing member with a developer.
2. Description of Related Art
The prior art and problems peculiar thereto will hereinafter be described with reference to FIG. 9 of the accompanying drawings. FIG. 9 is an illustration of portions around a developing roller which is the developer carrying member of a developing apparatus according to the prior art.
In image forming apparatuses using the electrophotographic image forming process, use has heretofore been made of the process cartridge system in which a photosensitive drum and process means for acting on the photosensitive drum are integrally made into a cartridge which is made detachably attachable to the main body of an image forming apparatus. According to this process cartridge system, the maintenance of the apparatus can be done by a user himself without resort to a serviceman and therefore, the operability of the apparatus could be markedly improved. So, this process cartridge system is widely used in image forming apparatuses.
Recently there have been produced many such process cartridges available for use in color image forming apparatuses. A higher quality of image than before will be expected of image forming apparatuses in the future including such color image forming apparatuses.
On the other hand, in a developing apparatus using a non-magnetic toner, the electrification charge amount of the developer (toner) on a developing roller has been liable to become unstable depending on the environment (such as temperature and humidity) in which it is placed, and it has sometimes affected the quality of image.
In order to mitigate such influence of the environment, there has heretofore been adopted means such as regulating a developing bias value in conformity with the environment. Also, recently, in order to enable the electrifying charge amount of the toner on the developing roller to be obtained stably without being affected by such environmental factors, use has come to be made of a toner electrifying roller or the like which is a developer electrifying member.
The toner electrifying roller is in contact with the developing roller and uniformly imparts charges to the toner on the developing roller while being driven to rotate thereby. Also, the toner electrifying roller has its outer peripheral surface pressurized by a torsion coil spring or the like, whereby there has been adopted a construction in which it contacts with the developing roller and is driven to rotate thereby.
As shown in FIG. 9, however, there has been adopted a construction in which a conventional toner electrifying roller 102 has its outer peripheral surface pressurized by a torsion coil spring 103 or the like, whereby it is pressed against a developing roller 101 and is driven to rotate thereby and therefore, when the balance between the resistance by the pressure force of the spring 103 and the frictional force with the developing roller 101 through a toner layer is destroyed, bad rotation or the like may occur and it may cause the aggravation of the quality of image.
As an example of using a toner electrifying roller is disclosed in U.S. Pat. No. 6,411,791.
It is an object of the present invention to provide a developing apparatus in which the pressure of a developer electrifying member to a developer carrying member is stabilized.
It is another object of the present invention to provide a developing apparatus in which charges are uniformly imparted to a developer carried on a developer carrying member by a developer electrifying member.
It is still another object of the present invention to provide a developing apparatus in which a developer electrifying member can be made stably rotatable.
It is yet still another object of the present invention to provide a developing apparatus in which a developer electrifying member can be stably held.
Further objects and features of the present invention will become more fully apparent from the following detailed description when re and with reference to the accompanying drawings.